The present invention relates to a method of fixing a stator core and an electric compressor with a motor using the method.
Referring to FIG. 6, a stator 100 of a motor is shown which is fixed inside a cylindrical housing 150. A stator core 110 of the stator 100 is formed of a plurality of stator core sheets 111 laminated together into a stack (refer to FIG. 7). It is noted that stator windings are not shown in FIG. 6.
Referring to FIG. 7 showing a process of making a stator core sheet 111, a common electromagnetic steel sheet 160 is rolled to a predetermined thickness. Each of the stator core sheets 111 is blanked off from the steel sheet 160 by using a die. A predetermined number of the stator core sheets 111 are laminated to form the stator core 110.
Referring to FIG. 8, there exists a variation in the thickness of the steel sheet 160 in the direction perpendicular to a rolling direction of the steel sheet 160. In making the stator core 110 which requires perpendicularity, the blanked stator core sheets 111 are turned and laminated one on another so that the perpendicularity is accomplished.
Referring back to FIG. 6, the stator core 110 has on the inner circumferential surface thereof a plurality of teeth 110A, around each of which a copper wire (not shown) is wound thereby to form the stator 100 of the motor. The copper wires are insulated from the teeth 110A. The stator 100 is fixed inside the housing 150 by any suitable method such as shrink fit. As shown in FIG. 6, the stator 100 is fixed over the entire circumference by the housing 150.
Japanese Patent Application Publication No. 10-24333 discloses a method of manufacturing a stator core sheet whose axial contour is circular or a true circle. Specifically, a blanking die is controlled such that a stator core sheet having a true circle is made by correcting an elliptical shape of the stator core sheet elongated in the direction perpendicular to the rolling direction of electromagnetic steel sheet and contracted in the rolling direction. Japanese Patent Application Publication No. 2006-299834 discloses an electric compressor having a housing whose inner circumferential surface is formed with a plurality of projections by which the stator of an electric motor for the compressor is fixed to the housing.
A stator core sheet 111 blanked from the steel sheet 160 by using a die is strained, as shown in FIG. 9. FIG. 9 shows an outside contour of the die for blanking the stator core sheet 111 from the steel sheet 160 and an outside contour of the blanked stator core sheet 111. While the outside contour of the die is circular, the outside contour of the blanked stator core sheet 111 is elliptical. That is, the outside contour of the stator core sheet 111 cut by a circular blanking die is elliptical. More specifically, the stator core sheet 111 may be formed such that its outside diameter is increased in the rolling direction of the steel sheet 160 and decreased in the direction perpendicular to the rolling direction. Alternatively, the stator core sheet 111 may be formed such that its outside diameter is decreased in the rolling direction of the steel sheet 160 and increased in the direction perpendicular to the rolling direction.
Because the strain of the stator core sheets 111 blanked off from the electromagnetic steel sheet 160 varies from one production lot to another, it is necessary for a manufacturer of the stator core 110 to control the dimension of the outside diameter of the stator core sheets 111. Therefore, it is necessary for the manufacturer to make adjustment of dies for minimizing the number of stator core sheets falling outside the tolerance and for ensuring the process capability.
The outer circumferential surface of the housing 150 may have a flat portion formed by planing, on which a sensor is mounted. However, fixing the stator 100 in the housing 150 with the outer circumferential surface of the stator core 110 strained, the flatness of the flat portion deteriorates. If the sensor is mounted on such a deteriorated flat portion, the sensor may not function properly due to poor sensitivity. In order to avoid such problem, the stator 100 is firstly fixed in the housing 150 and then any appropriate provision is made to prevent foreign matters from entering into the housing 150 before performing the planing for the flat mounting portion for the sensor.
Referring to FIGS. 6 and 10, the strained stator core sheets each having 18 slots are turned for each 60 degrees in laminating such sheets one another thereby to form a laminated stator core. If such a stator core 110 is fixed in the housing 150 by shrink fit, the contact area between the inner circumferential surface of the housing 150 and the outer circumferential surface of the stator core 110 is smaller than that in the case where the axial contour of the stator core 110 is a true circle. As a result, there is fear that the stator 100 is rotated because the fixation of the stator 100 to the housing 150 fails to resist the torque of the motor operating under a high load.
The present invention is directed to a method of fixing a stator core in a housing without being influenced by the strain of stator core sheets and with little deformation to the housing after assembling. In addition, the present invention is directed to an electric compressor with a motor using the method.